FIG. 1 illustrates a diagram showing a related art device for controlling supply of current and static capacitance to a compressor.
Referring to FIG. 1, a related art device for controlling supply of current and static capacitance to a compressor is provided with a utility power supply 1, a first relay 2 for being turned on/off in response to a control signal from the compressor, a reactor 3 for absorbing a reactive power from the utility power supplied through the utility power supply 1 according to the turning on/off operation of the first relay 2, and providing the utility power to a main winding C1 of a compressor motor ‘M’, a second relay 4 for monitoring a voltage on the reactor 3, a first contact 4a connected parallel to the third reactor 3 for being opened or closed by the second relay 4, an operating capacitor 5 connected in parallel to the third reactor 3, a starting capacitor 6 connected in parallel with the operating capacitor 5, a third relay 7 for monitoring a voltage at starting, a second contact 7a fitted to a fore end of the second relay 4 for being opened or closed by the third relay, and a third contact 7b fitted to a rear end of the starting capacitor.
The operation of the foregoing related art device will be explained.
Upon application of the control signal from the compressor, the first relay 2 is turned on, to supply a power to the main winding C1 of the compressor motor ‘M’ through the third reactor 3. In this instance, the third reactor 3 removes a reactive power from the power to the main winding. On the other hand, the utility power is supplied to a supplementary winding of the compressor motor ‘M’ through the parallel circuit of the operating capacitor 5 and the starting capacitor 6 as the third contact 7b is closed. Referring to a region 8 in FIG. 1, at an initial starting of the compressor, since the compressor motor ‘M’ is not rotated, a voltage to the third relay 7 is too low to put the third relay 7 into action. And, if the compressor motor ‘M’ becomes to rotate at a revolution higher than a preset value as the voltage on the third relay 7 rises according to the rotation of the compressor motor ‘M’, the third relay 7 comes into action, to close the second contact 7a and to open the third contact 7b. Since the second relay 4 comes into action as the second contact 7a is closed, the first contact 4a is closed to turn off the third reactor 3 and to open the third contact 7b, to isolate the starting capacitor from the circuit. That is, at the moment of starting, the third reactor 3 becomes to be connected to the compressor motor ‘M’ in series to limit an excessive current, and the starting capacitor 6 provides a greater capacitance to the supplementary winding C2 to improve starting characteristics of the compressor.
However, the related art device for controlling supply of current and static capacitance to a compressor has the following disadvantages.
First, there have been frequent troubles in the region 8 at which a starting capacitance is controlled.
Second, the mechanical system of the device for supplying power to the compressor costs high.
Third, the starting control by the voltage rise following rotation of the compressor motor ‘M’ can not define a starting current accurately and has a poor starting characteristic.
Fourth, the generation of excessive current in starting of the compressor actuates the circuit breaker, gives bad influences to peripheral device of the compressor, and has inconvenience in restoring the compressor to an original state.